A progressive teachers' union on Wednesday filed a petition with the national human rights watchdog, demanding the education ministry cancel moves to discipline and seek the criminal punishment of union members for taking part in political protest.

Early this month, the ministry asked prosecutors to investigate 36 teachers who led strike action last month and 71 union officials accused of preparing an anti-government statement on behalf of more than 10,000 teachers.

The government has claimed the teachers violated their duty to maintain political neutrality and a ban on political activities by civil servants.

"Teachers' freedom of expression should be respected in principle as a basic value of democracy," the Korean Teacher and Education Workers Union  said in a statement read during a news conference in front of the National Human Rights Commission's office in central Seoul.

"The government's demand for criminal punishment against teachers simply because they signed their name on the political statement and took part in a protest rally is tantamount to a measure tearing down democracy and reverting to the country's authoritarian past," it said.

On June 27, about 1,500 KTU members around the nation collectively took unauthorized leave from work in protest of what it called the government's oppression of the union.

A local administrative court ruled in favor of the government's decision to deprive the union of its 14-year-old status as a legal trade union for having dismissed educators among its members.

Some 12,000 teachers later issued the "Teachers' Declaration" denouncing the government for its poor handling of April's ferry disaster that killed more than 300 people, mostly high school students on a school trip. (Yonhap)